Fix checking for expression indexes support

lib/active_record_doctor/detectors/missing_unique_indexes.rb

@@ -66,7 +66,7 @@ def validations_without_indexes
             case_sensitive = validator.options.fetch(:case_sensitive, true)
 
             # Avoid a false positive if expression indexes are unsupported.
-            next if !case_sensitive && Utils.expression_indexes_unsupported?
+            next if !case_sensitive && !connection.supports_expression_index?
 
             validator.attributes.each do |attribute|
               columns = resolve_attributes(model, scope + [attribute])

lib/active_record_doctor/utils.rb

@@ -14,12 +14,6 @@ def mysql?(connection = ActiveRecord::Base.connection)
       def sqlite?(connection = ActiveRecord::Base.connection)
         connection.adapter_name == "SQLite"
       end
-
-      def expression_indexes_unsupported?(connection = ActiveRecord::Base.connection)
-        sqlite?(connection) ||
-          # Active Record is unable to correctly parse expression indexes for MySQL.
-          (mysql?(connection) && ActiveRecord::VERSION::STRING < "7.1")
-      end
     end
   end
 end

test/setup.rb

@@ -146,7 +146,7 @@ def require_non_key_index_columns!
   end
 
   def require_expression_indexes!
-    skip("#{current_adapter} doesn't support expression indexes") if ActiveRecordDoctor::Utils.expression_indexes_unsupported?
+    skip("#{current_adapter} doesn't support expression indexes") if ActiveRecord::Base.connection.supports_expression_index?
   end
 
   def require_non_indexed_foreign_keys!